Medical Device With Intra-Conductor Capacitive Energy Storage

ABSTRACT

A medical device, such as for electrical stimulation, includes an electronic circuit that is implantable at a first location in an animal. The electronic circuit has an element for receiving a wireless signal and a power supply that converts electrical energy from that signal into a supply voltage for powering the medical device. An electrical lead, that extends from the electronic circuit through the animal, has a first conductor, a second conductor, and a plurality of capacitors connected between those conductors to store the supply voltage. An electrode is implanted in the animal and is connected to the electronic circuit by a third conductor. In one embodiment, the third conductor extends through the electrical lead electrically isolated from the capacitors, and in another embodiment, the third conductor is physically separate from the electrical lead.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation in part of U.S. patent application Ser. No. 11/089,476 filed on Mar. 24, 2005.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to implantable medical devices that produce electrical pulses which stimulate organs of an animal, and more particularly to the storage of energy in such medical devices.

2. Description of the Related Art

A remedy for people with slowed or disrupted natural heart activity involves implanting a cardiac pacing device which is a small electronic apparatus that stimulates the heart to beat at regular rates.

Typically the pacing device is implanted in the animal's chest and has sensor electrodes that detect electrical impulses associated with in the heart contractions. These sensed impulses are analyzed to determine when abnormal cardiac activity occurs, in which event a pulse generator is triggered to produce electrical pulses using power from a battery. Wires carry these pulses to electrodes placed adjacent specific cardiac muscles, which when electrically stimulated contract the heart chambers. It is important that the stimulation electrodes be properly located to produce contraction of the heart chambers.

Modern cardiac pacing devices vary the stimulation to adapt the heart rate to the animal's level of activity, thereby mimicking the heart's natural action. The pulse generator modifies that rate by tracking the activity of the sinus node of the heart or by responding to other sensor signals that indicate body motion or respiration rate.

U.S. Pat. No. 6,445,953 describes a cardiac pacemaker that has a pacing device, which can be located outside the animal, to detect abnormal electrical cardiac activity. When that occurs, the pacing device emits a radio frequency signal, which is received by a stimulator implanted in a vein or artery of the animal's heart. Specifically, the radio frequency signal induces a voltage pulse in an antenna on the stimulator and that pulse is applied across a pair of electrodes, thereby stimulating adjacent muscles and contracting the heart.

Although this cardiac pacing apparatus offered several advantages over conventional pacemakers, it required that sufficient energy be derived from the received radio frequency signal to power the implanted circuit and to stimulate the adjacent organ. The amount of energy required may be relatively great, especially when the medical device is an implantable defibrillator.

Therefore, it is desirable to provide an energy storage mechanism in the implanted apparatus which will accumulate energy from a radio frequency signal and provide that accumulated energy when needed for organ stimulation.

SUMMARY OF THE INVENTION

A medical device is provided to artificially stimulate an organ of an animal. That medical device includes a first electrode and a second electrode for implantation into the animal. An electrical lead, that extends through the animal, has a first conductor and a second conductor with a plurality of capacitors connected there between. The plurality of capacitors may be connected in parallel between the first and second conductors, in series, or groups may be formed by several capacitors connected in series with the groups then connected in parallel between the first and second conductors.

An element is provided for receiving wireless signals, which may be in the radio frequency spectrum, for example. A stimulation circuit implantable in the animal uses energy from a received wireless signal to charge the plurality of capacitors with electrical energy. In response to a trigger event, the stimulation circuit applies the electrical energy from plurality of capacitors across the first and second electrodes to electrically stimulate the organ of the animal.

In one embodiment of the medical device, the electrical lead has a third conductor which connects the first electrode to the stimulation circuit with the third conductor electrically isolated from the plurality of capacitors. In another embodiment the third conductor is physically separate from the electrical lead, which is used solely for energy storage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a medical device in the form of a cardiac pacing apparatus attached to an animal;

FIG. 2 shows the power transmitter circuitry of the cardiac pacing apparatus;

FIG. 3 is an perspective cut-away view of cardiac blood vessels in which a vascular stimulator and electrodes of the cardiac pacing apparatus have been implanted;

FIG. 4 is a block diagram of an electrical circuit in the vascular stimulator shown in FIG. 2;

FIG. 5 is a longitudinal cross sectional view through an electrical lead which contains energy storage capacitors according to the present invention;

FIG. 6 is a longitudinal cross sectional view through a second electrical lead which contains energy storage capacitors connected in series;

FIG. 7 is a longitudinal cross sectional view through a third electrical lead which contains groups of energy storage capacitors connected in series with the groups then connected in parallel;

FIG. 8 depicts an electrical circuit for another medical device which has a other types of an electrical leads that contain energy storage capacitors;

FIG. 9 is a schematic diagram of the circuit for a voltage intensifier in the intravascular medical device;

FIG. 10 depicts a exemplary voltage levels produced at output terminals of the voltage intensifier in different modes of operation;

FIG. 11 is a longitudinal cross sectional view through an electrical lead in FIG. 8;

FIG. 12 is a cross section view along line 12-12 in FIG. 11; and

FIG. 13 is a block diagram of an electrical circuit for a medical device that employs another type of electrical lead that contains energy storage capacitors.

DETAILED DESCRIPTION OF THE INVENTION

Although the novel energy storage mechanism for an implantable medical device is being described in the context of a cardiac pacing apparatus, it should be understood that the inventive concepts can be used in other types of apparatus.

With initial reference to FIG. 1, a medical device 10 electrically stimulates an animal's heart 12 to contract or to convert from fibrillation to a normal rhythm. That medical device comprises an external power source 14 and a stimulator 20 that is implanted in a blood vessel 18 of a muscle in the heart. As will be described in greater detail, the power source 14 transmits a radio frequency signal 16 which causes the stimulator 20 to emit an electric current that stimulates the heart muscle.

Referring to FIG. 2, the power source 14, that preferably is worn outside the animal's body adjacent the chest, in the illustrated embodiment comprises a conventional pacing signal generator 22 connected to cardiac activity sensing electrodes 23 attached to the animal's body. Alternatively, the power source 14 may be implanted in the animal. The internal circuitry and operation of the pacing signal generator 22 are similar to prior cardiac pacers. However, instead of the output stimulation signals being applied to the electrodes via leads, the pacing signals are applied to an input of a radio frequency (RF) transmitter 24. In response to the stimulation signal (also known as a pacing signal) from the generator 22, the radio frequency transmitter 24 emits a pulse of the radio frequency signal 16 that is transmitted throughout the animal's chest cavity via an antenna 26. Preferably the antenna 26 either is located relatively close to the heart 12 or is of a type which focuses the radio frequency signal toward the heart. Both the pacing signal generator 22 and the RF transmitter 24 are powered by a battery 28.

As illustrated in FIG. 3, the stimulator 20 is placed at a second location in an artery or vein 18 in close proximity to the atria or ventricles of the heart 12. For example the vascular stimulator 20 may be positioned in the coronary sinus vein. The stimulator 20 includes a support body 30 similar to well-known expandable vascular stents that are employed to enlarge a restricted vein or artery. The support body 30 has a generally tubular shape that initially is collapsed to a relatively small diameter enabling the stimulator to pass freely through blood vessels of an animal. The procedure for implanting the stimulator 20 is similar to that used for vascular stents. For example, a balloon at the end of a standard catheter is inserted into the stimulator 20 in a collapsed configuration. That assembly is inserted through an incision in a vein or artery near the skin of an animal and passed through the vascular system to the appropriate location proximate to the atria or ventricles of the heart 12. The balloon of the catheter then is inflated to expand the stimulator 20, thereby slightly enlarging the blood vessel 18 which embeds the stimulator in the wall of the vein or artery. The balloon is deflated, the catheter is removed from the animal, and the incision is closed. Alternatively, a self-expanding support body 30 may be utilized. The slight enlargement of the blood vessel 18 and the tubular design of the support body 30 allows blood to flow relatively unimpeded through the vascular stimulator 20.

With additional reference to FIG. 4, the stimulator 20 has a stimulation circuit 32 and a receive antenna 34 in the form of a wire coil wound circumferentially around the support body 30. The stimulation circuit 32 includes an RF signal detector 38 having an input connected to the receive antenna 34 and tuned to the frequency of the RF signal 16 that is emitted by the power source 14. The RF signal detector 38 converts the energy of that RF signal into an electric voltage that charges a storage capacitor 40 which supplies electrical power to the circuitry on the vascular stimulator 20. The periodic pulses of the RF signal charge the storage capacitor 40 so that it will have sufficient stored energy when stimulation of the heart is required.

One electrode 36 in the form of a ring encircles the support body 30 is connected to one terminal of the storage capacitor 40. Another electrode 44 is adjacent to the wall of a blood vessel 46 at a second location of the heart, as seen in FIG. 3, and is coupled to the stimulation circuit 32 by an insulated electrical lead 47 extending through the blood vessels. The relatively small size of the other electrode 44 allows it to be placed into a significantly smaller blood vessel 46 than the vascular stimulator 20. As a result, that electrode 44 can be placed is a greater variety of locations in the cardiac vascular system and in close proximity to the muscles that contract the desired portion of the heart 12.

In order to provide enough electrical energy for stimulation, especially for defibrillation, as relatively large storage capacitance is required. Instead of placing that capacitance on the support body 30 of the stimulator 20, a plurality of capacitors are placed along the length of the electrical lead 47 that connects the first electrode 44 to the stimulation circuit 32. With reference to FIG. 5, the electrical lead 47 has a tubular shell 50 of insulated material with two conductors 51 and 52 extending longitudinally along a central opening in the shell. A plurality of disk-shaped capacitors 54 also are spaced along that central opening. These capacitors 54 may be conventional surface mount type devices, such as model PCC2232CT which is a 4.7 μf, 16 WVDC capacitor available from Panasonic Corporation of North America in Secaucus, N.J., U.S.A. The terminal on one side of each capacitor 54 is connected to the first electrical conductor 51 and the other terminal is connected to the second conductor 52. Therefore, the plurality of capacitors 54 are connected in parallel so that the individual capacitances are summed to form a large equivalent storage capacitor 40.

FIG. 6 illustrates an alternative structure for the electrical lead 47 which has a tubular insulated shell 60 with first and second conductors 61 and 62 extending longitudinally along the central opening. A plurality of disk-shaped capacitors 64 are connected in series between the first and second conductors 61 and 62, in contrast with electrical lead 47 in which the capacitors 54 are connected in parallel.

FIG. 7 illustrates a third structure for the electrical lead 47 which has an tubular insulated shell 70 with a the central opening in which first and second conductors 71 and 72 longitudinally extend. A plurality of disk-shaped capacitors 73-79 are located within the central opening. The capacitors are connected in groups with the devices in each group being coupled in series and the groups connected in parallel to the first and second conductors 71 and 72. Specifically, one group comprises capacitors 73, 74 and 75 that are connected in series with the first capacitor 73 in that group having a terminal that is coupled to the first conductor 71 and the last capacitor 75 in that group having a terminal that is coupled to the second conductor 72. Another group comprises capacitors 76, 77 and 78 connected in series with the first capacitor 76 coupled to the first conductor 71 and the last capacitor 78 coupled to the second conductor 72. The number of capacitors in each group and the number of groups are chosen to provide the desired cumulative capacitance and working voltage for the storage capacitor 40 of the stimulator 20.

Referring again to FIG. 4, the power source 14 periodically transmits the radio frequency signal 16 to the stimulator 20. The RF signal detector 38 derives electrical voltage from the energy of that RF signal and applies that voltage across conductors 51 and 52 to charge the plurality of individual capacitors that cumulatively form the storage capacitor 40. Thus a sufficient charge is maintained on the storage capacitor 40 for when cardiac stimulation is needed.

The power source 14 also responds to the electrical signals from the heart, that are detected by the sensing electrodes 23, by determining in a conventional manner when cardiac stimulation is required. When stimulation is to occur, the RF transmitter sends a uniquely shaped RF signal pulse sequence. The RF signal detector 38 in FIG. 4 responds to that RF signal pulse sequence by activating a pulse circuit 42 that closes a switch 45 connected to a second electrode. That action completes a circuit thereby dumping the voltage stored on the capacitor across the first and second electrodes 36 and 44 which stimulates the heart tissue between those electrodes.

With reference to FIG. 8, an alternative embodiment of a stimulator type medical device includes a receive antenna 82 that is tuned to pick-up the radio frequency signal 16. However, unlike the previous medical device in FIGS. 2 and 4, the power source 14 for this embodiment transmits a radio frequency signal that primarily provides only electrical power to the second stimulator 80. Here the power source 14 does not have the pacing signal generator 22 and sensing electrodes 23 as the functions of those components have been integrated into the implanted second stimulator as will be described. When necessary, the radio frequency signal 16 also carries control commands and data that specify operational parameters of the second stimulator 80, such as the duration of a stimulation pulse that is applied to a pairs of stimulation electrodes 44 and 48 implanted close to each other in a blood vessel 46, as shown in FIG. 3.

In the second stimulator 80, the receive antenna 82 is located remotely from the stimulation circuitry 81 mounted on the stimulator support body 30, such as on a separate expandable body, similar to support body 30 and coupled by a lead 83 to stimulation circuitry 81 mounted on the support body 30. The stimulation circuitry 81 includes a signal discriminator 84 which has a data detector 85 that recovers data and commands carried by the radio frequency signal 16 and sends that information to a control circuit 86 for storage and subsequent use in operating the stimulator. Preferably, the control circuit 86 comprises a conventional microcomputer with analog and digital input/output circuits and an internal memory which stores a software control program and data gathered and used by that program.

The control circuit 86 also has an input coupled to a pair of sensor electrodes 87 that detect electrical activity of the heart 12 and provide conventional electrocardiogram signals which are utilized to determine when cardiac pacing should occur. Additional sensors for other physiological characteristics, such as temperature, blood pressure or blood flow, may be provided and connected to the control circuit 86. The stimulation electrodes 44 and 48 also can be used to sense electrical activity of the heart. For that purpose the first and second stimulation electrodes 44 and 48 are connected to inputs of an instrumentation amplifier 88 that has an output coupled to an analog input of the control circuit 86 and to an input of a differentiator 89. The differentiator 89 has another input which receives a reference voltage (REF) which enables signal transition detection to provide an input signal to the controller 53 indicating events in the sensed cardiac activity. For example, the differentiator 89 in conjunction with software executed by the control circuit 86 determine the heart rate based on the number of cardiac signal transitions counted over a defined time interval. The control circuit 86 initiates cardiac pacing when the heart rate goes out of a normal range for a given length of time.

The software executed by the control circuit 86 analyzes the electrocardiogram signals and other physiological characteristics from the electrodes to determine when to stimulate the animal's heart 12. When that analysis indicates that stimulation is required, the control circuit 86 issues a command to the stimulation signal generator 90 that responds by applying one or more pulses of voltage across the first and second electrodes 44 and 48. The stimulation signal generator 90 controls the intensity and shape of the pulses. The output pulses from the stimulation signal generator 90 can be applied either directly to those electrodes 44 and 48 or via an optional voltage intensifier 91. With additional reference to FIG. 3, note that the first and second electrodes 44 and 48 are implanted remotely from the support body 30 on which the stimulation circuitry 81 is mounted.

The voltage intensifier 91 preferably is a “flying capacitor” inverter that charges and discharges in a manner that essentially doubles the power. This type of device has been used in integrated circuits for local generation of additional voltage levels from a single supply voltage. FIG. 9 illustrates a voltage intensifier 91 with a single doubler stage 120 and an inverter stage 122. Various numbers of doubler stages 120 can be concatenated to increase a DC supply voltage (VDC) from a power supply 92 in FIG. 8 to the desired stimulation output voltage. The number of doubler stages may be switchably selected in response to control signals from the stimulation signal generator, thereby enabling the voltage to be increased by different powers of two and inverted or not inverted. When there are more that two stimulation electrodes, a switching network is provided at the output of the voltage intensifier 91 to selectively apply the final output voltage across one pair of those electrodes.

The doubler stage 120 includes two pairs of switches that are operated by a switch controller 124 in response to control signals received from the stimulation signal generator 90. The first pair of switches S1A and S1B is connected to a first side of an input capacitor 126. Switch S1A connects and disconnects the first side of the input capacitor 126 to the positive power supply terminal, and switch S1B connects and disconnects the first side of the input capacitor to a first intermediate node 128. Switch S2A connects and disconnects a second side of input capacitor 126 to the negative power supply terminal, and switch S2B connects and disconnects the second side of the input capacitor to the positive power supply terminal. The negative power supply terminal also is directly connected to a second intermediate node 129. The term “directly connected” as used herein means that the associated components are connected together by a conductor without any intervening element, such as a switch or impedance, that controls or restricts the flow of electric current, beyond the intrinsic impedance of any conductor. A doubler capacitor 127 is connected across the first and second intermediate nodes 128 and 129.

The intermediate nodes 128 and 129 are coupled to the input of the inverter stage 122, which has third and fourth switches S3 and S4 operated in unison by the switch controller 124. The third switch S3 alternately connects the first side of an inverter capacitor 130 to the first intermediate node 128 or to a first output terminal 134. The first output terminal 134 also is directly connected to the second intermediate node 129. The fourth switch S4 alternately connects a second side of the inverter capacitor 130 to the negative power supply terminal or to a second output terminal 135. A fifth switch S5 selectively connects the first intermediate node 128 to the first output terminal 134. An output capacitor 132 is coupled between the first and second output terminals 134 and 135 to which the stimulation electrodes 44 and 48 are connected. The value of the output capacitor is based on the specific intended use. For example, in fast switching applications one may use a smaller capacitance, while a larger value may be used for a slow switching application.

When stimulation is to occur, the control circuit 86 in FIG. 8 activates the stimulation signal generator 90. In response, the stimulation signal generator 90 issues an INTENSITY command to the switch controller 124 in the voltage intensifier 91 specifying the magnitude of the stimulation voltage. For example, that magnitude may be one or two times the supply voltage VDC. The stimulation signal generator 90 responds to the INTENSITY command by operating the switches within the voltage intensifier 91 in the appropriate manner to apply stimulation pulses of the specified magnitude, as will be described. The polarity of the voltage pulses applied across the stimulation electrodes 44 and 48 also can be selected by enabling or disabling the inverter stage 122. When the voltage intensifier 91 has multiple doubler stages 120, the INTENSITY command determines the number of those stages that are active in order to produce the specified voltage magnitude. The stimulation signal generator 90, then initiates a pulse or a sequence of pulses by sending one or more PULSE commands to the voltage intensifier 91.

If the specified voltage magnitude is VDC, the doubler stage 120 is configured by closing switches S1A and S1B and opening switch S2A. Switch S2B may be in either state. In the inverter stage 122, the fifth switch S5 is closed and the third and fourth switches S3 and S4, that are operated in unison, may be in either position. This configuration applies the supply voltage VDC directly to the output terminals 134 and 135 of the voltage intensifier 91, as depicted during period P1 in FIG. 10 in which the second output terminal 135 is positive with respect to the first output terminal 134. The fifth switch S5 or one of switches S1A and S1B in the doubler stage 120 is opened to terminate each voltage pulse applied to the stimulation electrodes 44 and 48.

When voltage is not to be applied to the stimulation electrodes 44 and 48 for a prolonged period, all the switches in the voltage intensifier 91 are opened, thereby applying zero volts across those electrodes, as depicted during period P2 in FIG. 10.

The inverse voltage level, i.e. −VDC, can be applied across the output terminals 134 and 135. This is accomplished by configuring the doubler stage 120 by closing switches S1A and S1B and opening switch S1A. Switch S2B maybe in either state. The inverter stage 122 is configured by opening the fifth switch S5. Initially the third and fourth switches S3 and S4 are placed in the state illustrated in FIG. 9 so that the voltage across the first and second intermediate nodes 128 and 129 charges the inverter capacitor 130. Then the positions of the third and fourth switches S3 and S4 are changed simultaneously to dump the accumulated charge across the first and second output terminals 134 and 135. This applies a negative VDC to those output terminals as depicted during period P3 in FIG. 10.

The voltage doubler stage can be activated to apply a voltage level across the first and second intermediate nodes 128 and 129 that is twice the supply voltage VDC. This is accomplished by alternately charging and discharging the input capacitor 126 with the supply voltage VDC. When the switches S1A and S2A are closed while switches S1B and S2B are opened as shown in FIG. 9, the input capacitor 126 charges to the supply voltage VDC level. Then the states of those four switches S1A, S1B, S2A and S2B are reversed to apply that charge to the doubler capacitor 127, thereby adding to the voltage already across the doubler capacitor. The four switches are then returned to their original states to recharge the input capacitor 126. This operation is rapidly repeated again and again. This produces a voltage V1 across the intermediate nodes 128 and 129 that is twice the supply voltage (i.e. 2VDC). In the inverter stage 122, the fifth switch S5 is closed and the third and fourth switches S3 and S4, that are operated in unison, may be in either position. This configuration applies the doubled supply voltage 2VDC directly to the output terminals 134 and 135 of the voltage intensifier 91 as depicted during period P5 in FIG. 10.

The inverter stage 122 can be employed to reverse the polarity of the doubled supply voltage. Here, the doubler stage 120 is operated as described immediately above to produce the 2VDC level at the first and second intermediate nodes 128 and 129. However, the inverter stage 122 now is configured by opening the fifth switch S5. Initially the third and fourth switches S3 and S4 are placed in the state illustrated in FIG. 9 so that the voltage across the first and second intermediate nodes 128 and 129 charges the inverter capacitor 130. Then the positions of the third and fourth switches S3 and S4 are changed simultaneously to dump the accumulated charge across the first and second output terminals 134 and 135. This applies −2VDC across those output terminals as depicted during period P7 in FIG. 10.

With reference again to FIG. 8, the stimulation circuitry 81 also comprises components for supplying power for the production of the stimulation pulses. For that purpose, the signal discriminator 84 includes the power supply 92 that extracts energy from the received radio frequency signal 16. Specifically, the radio frequency signal is rectified to produce the DC supply voltage (VDC) which charges a storage capacitor 95 in the same manner as storage capacitor 40 in FIG. 4.

However, for the second stimulator 80, the terminals of the storage capacitor 95 are not connected directly to either the first or second stimulation electrodes 44 or 48. Instead, the storage capacitor 95 is coupled to the power supply 92 by separate first and second conductors 101 and 102. Now, the first stimulation electrode 44 is connected to a third conductor 96 that extends through an electrical lead 97 in which the individual capacitors that form the storage capacitor 95 are located. The electrical lead 97 extends from the stimulation circuitry 81 through the vasculature of the animal. A fourth conductor 98 also extends through the electrical lead 97 connecting the second stimulation electrode 48 to the stimulation circuitry 81. Alternatively the fourth conductor 49 may be totally separate from the electrical lead 97.

Referring to FIGS. 11 and 12, a plurality of capacitors 104 are placed along the length of the electrical lead 97 that connects the first electrode 44 to the voltage intensifier 91. The electrical lead 97 has a tubular shell 100 of electrical insulating material with the first and second conductors 102 and 103 extending longitudinally along a central opening in the shell. A plurality of disk-shaped capacitors 104 also is spaced along that central opening. These capacitors 104 are similar to the individual capacitors described with respect to FIG. 5. The terminal on one side of each capacitor 104 is connected to the first electrical conductor 102 and the other terminal is connected to the second conductor 103. Therefore, the plurality of capacitors 104 are connected in parallel so that the individual capacitances are summed to form a large equivalent storage capacitor 95. Alternatively, the individual capacitors 104 may be connected in series between the first and second conductors 102 and 103 similar to that shown in FIG. 6, or in serially groups that in turn are connected in parallel as in FIG. 7.

The third conductor 96, that connects the first electrode 44 to the stimulation circuitry 81, extends longitudinally through an electrical lead 97 along an inside surface of the tubular shell 100 and spaced from the plurality of capacitors 104 as seen in FIGS. 11 and 12. The fourth conductor 98 for the second stimulation electrode 48 also could extends longitudinally through the electrical lead 97 along an inside surface of the tubular shell 100 diametrically opposite to the third conductor 96. The third and fourth conductors 96 and 98 are electrically isolated from the storage capacitor 95 formed by the plurality of individual capacitors 104. Alternatively when the two stimulation electrodes 44 and 48 are space relatively far apart, the fourth conductor 98 for the second stimulation electrode 48 is separate from the electrical lead 97.

As a further variation, the plurality of capacitors that form a storage capacitor 95′ can be incorporated into the lead 83 that couples the receive antenna 82 to the stimulation circuitry 81, in which case the lead 83 has four conductors, two for the receive antenna and two separate conductors for the capacitors. In these implementations of the present invention, the storage capacitor 94 is incorporated into a lead that also has one or more separate conductors that carry signals between the stimulation circuitry 81 and a functional device, such as a stimulation electrode 44 or the receive antenna 82. To provide a relatively large storage capacitance, separate pluralities of capacitors can be placed in multiple leads of the medical device and connected in parallel.

FIG. 13 depicts another stimulator 110 type a medical device that is similar to stimulator 80 in FIG. 8 with like components being assigned identical reference numerals. The difference being that stimulator 110 has the storage capacitor 112 integrated into an electrical lead 114 that is physically separate from the electrical leads 116 and 118 for the first and second stimulation electrodes 44 and 48, respectively. The electrical lead 114 has an internal structure that is the same as any one of the leads in FIGS. 5-7 in which a plurality of individual capacitors are connected to first and second conductors.

The foregoing description was primarily directed to preferred embodiments of the invention. Even though some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure. 

1. A medical device, for implantation into an animal, comprising: an electronic circuit implantable at one location in the animal and having an element for receiving a wireless signal and a power supply that extracts electrical energy from the wireless signal in order to power the medical device; an electrical lead extending outward from the electronic circuit through the animal and having a first conductor and a second conductor coupled to the power supply with a plurality of capacitors connected to the first and second conductors, wherein the plurality of capacitors store the electrical energy; a first electrode for implantation at another location in the animal remote from the one location; and a third conductor connecting the first electrode to the electronic circuit.
 2. The medical device as recited in claim 1 wherein the electronic circuit responds to a trigger event by applying the electrical energy from the plurality of capacitors to the first electrode stimulate an organ of the animal.
 3. The medical device as recited in claim 1 wherein the third conductor extends through the electrical lead.
 4. The medical device as recited in claim 1 wherein the third conductor is physically separate from the electrical lead.
 5. The medical device as recited in claim 1 wherein the a signal conductor extends through the electrical lead and connects the element for receiving a wireless signal to other components of the electronic circuit.
 6. The medical device as recited in claim 1 wherein the electrical lead comprises a shell extending around the first conductor, the second conductor, and the plurality of capacitors.
 7. The medical device as recited in claim 1 wherein the plurality of capacitors is connected in parallel between the first and second conductors.
 8. The medical device as recited in claim 1 wherein the plurality of capacitors is connected in series between the first and second conductors.
 9. The medical device as recited in claim 1 wherein the plurality of capacitors are divided into groups with the capacitors in each group connected in series and the groups connected in parallel between the first and second conductors.
 10. The medical device as recited in claim 1 wherein the wireless signal is a radio frequency signal.
 11. The medical device as recited in claim 1 further comprising: a second electrode for implantation in the animal; and a fourth conductor physically separate from the electrical lead and connecting the second electrode to the electronic circuit.
 12. A medical device comprising: a first electrode for implantation at a first location in an animal; a second electrode for implantation into the animal; an electrical lead having a first conductor, a second conductor, a plurality of capacitors connected to the first and second conductors, and a third conductor is connected to the first electrode; an element for receiving a wireless signal; and a stimulation circuit for implantation at a second location in the animal and connected to the electrical lead, the second electrode and the element, the stimulation circuit using energy from the wireless signal to charge the plurality of capacitors with electrical energy, and responding to a trigger event by applying the electrical energy from the plurality of capacitors to the first electrode and the second electrode to electrically stimulate the animal.
 13. The medical device as recited in claim 12 wherein the plurality of capacitors is connected in parallel between the first and second conductors.
 14. The medical device as recited in claim 12 wherein the plurality of capacitors is connected in series between the first and second conductors.
 15. The medical device as recited in claim 12 wherein the plurality of capacitors are divided into groups with the capacitors in each group connected in series and the groups connected in parallel between the first and second conductors.
 16. The medical device as recited in claim 12 wherein the electrical lead comprises a shell that extends around the first conductor, the second conductor, the third conductor, and the plurality of capacitors.
 17. The medical device as recited in claim 12 further comprising a second electrical lead having at least one signal conductor extending there through and connecting the element for receiving a wireless signal to the stimulation circuit.
 18. A medical device, for implantation into an animal, comprising: an element for receiving a wireless signal; a first electrode and a second electrode for implantation in the animal; a stimulation circuit for implantation at a location in the animal and connected to the element, the stimulation circuit having a power supply that extracts electrical energy from the wireless signal to provide a supply voltage for powering the medical device, and responding to a trigger event by applying an electrical pulse across the first electrode and the second electrode to electrically stimulate the animal; an electrical lead extending outward from the stimulation circuit through the animal and having a first conductor, a second conductor, and a plurality of capacitors connected to the first and second conductors, the first conductor and the second conductor being connected to the stimulation circuit to charge the plurality of capacitors with the supply voltage; a third conductor separate from the electrical lead and connecting the first electrode to the stimulation circuit; and a fourth conductor separate from the electrical lead and connecting the second electrode to the stimulation circuit.
 19. The medical device as recited in claim 18 wherein the plurality of capacitors is connected in parallel between the first and second conductors.
 20. The medical device as recited in claim 18 wherein the plurality of capacitors is connected in series between the first and second conductors.
 21. The medical device as recited in claim 18 wherein the plurality of capacitors are divided into groups with the capacitors in each group connected in series and the groups connected in parallel between the first and second conductors.
 22. The medical device as recited in claim 18 wherein the electrical lead comprises a shell that extends around the first conductor, the second conductor, and the plurality of capacitors.
 23. The medical device as recited in claim 18 further comprising at least one signal conductor extending through the electrical lead and connecting the element for receiving a wireless signal to other components of the stimulation circuit. 